M&I Week 2 Flashcards
Two Distinct Functions of Antibodies
Conferred by two distinct portions of the antibody. Variable region interacts with antigen. Constant region interacts with other components of the immune system, which mediate different effector functions of antibodies
Variable Region of the Antibody
Highly diverse among different antibodies and interacts with the antigen. Each antibody contains two that can bind with antigen
Number of Variable Regions in an Antibody
2
Constant Region of an Antibody and Isotypes
Each antibody has only one constant region and it interacts with other components of the immune system, which mediate distinct effector functions of antibodies. Comes in five different forms (IgM, IgG, IgA, and IgE), each specialized to activate distinct components of the immune system and thus elicit distinct effector functions
Number of Constant Regions in an Antibody
1 & 5 isotypes
B-Cell Differentiation
Naive B Cells start off with producing surface immunoglobulins of the IgM and IgD varieties (co-expressed). Upon antigen recognition and B Cell activation, these B cells might differentiate into plasma cells that secrete antibodies of the IgM variety. Can occur in a T Cell independent manner, but most require T Cell help
Somatic Hypermutation
Some activated B Cells that receive T Cell help will undergo somatic hypermutation that results in the introduction of point mutations within the variable region of the antibody, which ultimately results in the development of antibodies with increased affinity for antigen
Affinity Maturation of the Antibody Response
Somatic Hypermutation can lead to the development of antibodies with increased affinity for antigen, resulting in “affinity maturation of the antibody response”. Requires intimate interactions of B Cells with T Cells and of B Cells with antigens trapped by follicular dendritic cells in germinal centers of lymphoid organs
Germinal Center Reaction
Affinity maturation requires intimate interactions of B Cells with T Cells and B Cells with antigens trapped by follicular dendritic cells in germinal centers of lymphoid organs, a process referred to as the germinal center reaction
Class Switch Recombination
When B Cells switch their antibody class from IgM (and IgD) to one of the other classes, without altering their antigen-binding specificity, in a genetic process referred to as class switch recombination
Differentiation into Plasma Cells vs. Differentiation into Memory B Cells
Plasma cell differentiation is a terminal process, whereas memory B Cells can be reactivated by specific antigen and undergo further somatic hypermutation and class switch recombination
Shape of Antibodies
Y-shaped, the structure of the cell surface expressed form of an immunoglobulin is identical to that of the secreted form, except for a short hydrophobic portion in the carboxy terminus of the heavy chain that anchors the protein to the membrane
Number of Name of Polypeptide Chains (Antibodies)
Antibodies contain two types of polypeptide chains, termed a heavy (H) and light (L) chain. Each antibody contains two heavy chains and two light chains
How Are Heavy Chains Linked to Each Other
Disulfide bonds
How Are Heavy Chains Linked to Light Chains
Disulfide bonds
Two Types of Light Chains
Kappa and Lambda
Isotypic Exclusion
A given antibody contains either kappa or gamma light chains, but never one of each
What Determines the Class of an Antibody
The heavy chain of the antibody
Five Different Heavy Chains
Mu, delta, gamma, alpha, and episilon, which corresponds to the five classes of antibodies (IgM, IgD, IgA, IgE). Can also contain subtypes for each heavy chain
Two Isotypes of Antibody That Can Polymerize
IgM assembles as a pentamer and IgA can assemble as a dimer
J-Chain in Antibody Polymerization
Multimerization of IgM and IgA monomers is facilitated by interaction of a polypeptide called a J-Chain, with cysteine residues in the “tailpiece” of IgM and IgA
Functions of Multimer Antibodies (IgM and IgA)
IgM is the first antibody class to be synthesized and its pentameric form permits high avidity interactions with antigen; IgA plays an important role in mucosal immunity and its transport across mucosal membranes requires dimerization (usually present as a monomer in the blood and lymph)
H and L Chains Contain Multiple Domains of What Length and What Structure
110 amino acids in length which fold into a structure referred to as a Beta-Barrel (two anti-parallel Beta-sheets connected by a disulfide bond)
Immunoglobulin Fold
The particular beta-barrel structure adopted by an immunoglobulin domain. This type of fold is quite popular among proteins of the immune system (as well as the nervous system)
Which Termini of Heavy and Light Chains Are Highly Variable
The amino-termini of both the heavy and light chains of immunoglobulins are highly variable
Variable Domains of Heavy and Light Chains
Variability predominantly contained within the N-terminus immunoglobulin domains of the heavy and light chains, which are referred to as the variable domains of the heavy and light chains, Vh and Vl, and together form the variable region of an antibody
Constant Domains of the Heavy and Light Chains
The constant domains of the heavy and light chains (Ch and Cl) together form the constant domain of the antibody molecule. Individual domains within the constant region of the heavy chain are referred to as Ch1, Ch2, and so on
Papain
Protease that cleaves antibodies just above the disulfide bonds that connect the two heavy chains together, resulting in three fragments: two fragments called Fab fragments (Fragment antigen binding), are identical and can each interact with antigen, and the third fragment, called the Fc fragment (Fragment cystallizable) mediates the effector functions of an antibody. Differences between distinct antibody classes are largely contained in the Fc portion of an antibody
Pepsin
This protease cleaves antibodies multiple times below the disulfide bonds that connect the two heavy chains, resulting in one main fragment, the F(ab’)2 fragment, which contains who Fab fragments (and thus two antigen-binding sites) linked by disulfide bonds, and multiple fragments derived from the Fc portion of an antibody
Recombinant DNA technology and Antibody Structure
Permits one to modify the structure of an antibody molecule, for example to attach the constant region of a human Ig-gamma chain gene to the variable region of a murine Ig-gamma chain, in order to convey human effector functions to an antibody generated in mice against a human therapeutic antigen
Hinge Region of an Antibody and Flexibility
Hinge region linked the two Fab fragments and the Fc portion. Other portions of the antibody molecule, such as the region between the variable and constant domains are also flexible. Permits antibodies to interact with multiple identical antigens that are spaced at a variable distance on a surface
What Biochemical Structures Can Antibodies Interact With
Proteins, carbohydrates, nucleic acids, lipids, and small molecules
Antigens
Any substance that can be recognized by an antibody. Most but not all antigens can induce an antigen specific immune response when introduced into (by immunization or vaccination, typically in the context of an adjuvant that induces activation of the innate immune system; AlOH) animals or human subjects
Immunogens
Antigens that can induce an antigen-specific immune response when introduced (by immunization or vaccination, typically in the context of an adjuvant that induces activation of the innate immune system) into animals or human subjects
Haptens
Antigens such as small organic chemicals (e.g trinitrophenol) can be recognized by antibodies but cannot elicit an antibody response when injected by themselves. Can be converted to immunogens by conjugating them to a carrier proteins
Hypervariable Regions
With regard to immunoglobulin heavy and light chains and stretches of amino acids, where variability is concentrated: Three highly variable regions, which can be identified in the variable region of both the heavy and light chains, separated from less variable regions (framework regions). Clustered within three loops at the outer edge of the immunoglobulin domain, forming the antigen-binding site
Framework Regions
Less variable regions and separated from the hypervariable regions, of which there are four in both the heavy and light chains
Complementary Determining Regions (CDRs)
Refers to the six hypervariable regions, as they form a surface complementary to the antigen. The third complementarity determining regions (CDR3), which have the highest variability, are most critical for interaction with antigen